The use of aerosol medication delivery systems to administer medication in aerosol form to a patient's lungs by inhalation is well known in the art.
Conventional aerosol medication delivery systems include pressurized metered-dose inhalers (pMDIs). Conventional pMDIs typically have two components: a canister component in which the medication particles are stored under pressure in a suspension or solution form and a receptacle component used to hold and actuate the canister. The canister component typically includes a valved outlet from which the contents of the canister can be discharged. Aerosol medication is dispensed from the pMDI by applying a force on the canister component to push it into the receptacle component thereby opening the valved outlet and causing the medication particles to be conveyed from the valved outlet through the receptacle component and discharged from an outlet of the receptacle component. Upon discharge from the canister, the medication particles are "atomized" forming an aerosol. It is intended that the patient coordinate the discharge of aerosolized medication with his or her inhalation so that the medication particles are entrained in the patient's inspiratory flow and conveyed to the lungs. Typically, pMDIs have used propellants, such as chlorofluorocarbons (CFCs), to pressurize the contents of the canister and to propel the medication particles out of the outlet of the receptacle component.
Although conventional pMDIs have been widely used to provide many patients with the benefits of aerosol medication, conventional pMDIs have certain drawbacks. For example, an objective of aerosol therapy has been the optimization of the mass percentage of the respirable dose of an aerosol medication in order to optimize deposition in a patient's lungs to achieve a full therapeutic effect with the least possible side-effects. Conventional pMDIs may not have always been able to meet this objective.
One drawback associated with conventional pMDIs relates to the discharge velocity of the aerosol particles. Medication particles are stored under considerable pressure in the pMDI canister and as a consequence, their velocity may be high upon discharge.
Among other things, the effect of high velocity contributes to a significant number of aerosol medication particles impacting and depositing in the patient's oropharynx and upper airway rather than continuing their pathway through the upper airway and into the lungs. Such impaction and deposition may result in a significant portion of the medication dose being systemically absorbed or ingested. As documented in the literature [J. L. Rau, "Respiratory Care Pharmacology", 4.sup.th ed. (1994, Mosby) at pp. 256-261; K. Meeran, A. Hattersley, J. Burrin, R. Shiner, K. Ibbertson K., "Oral and Inhaled Corticosteroids Reduce Bone Formation as Shown by Plasma Osteocalcin Levels", Am. J. Respir. Crit. Care Med 151:333-336], systemic absorption or ingestion of aerosol medication may cause a patient adverse side-effects, particularly when the aerosol medication is a corticosteroid. Some of these adverse side-effects include pharyngeal candidiasis, hoarseness, and adrenal suppression.
The high velocity of the aerosol medication particles may also accentuate the difficulty of a significant number of patients, particularly the very young and elderly, to coordinate actuation of the pMDI with inhalation of the aerosol medication particles generated. Failure to coordinate the actuation and inhalation maneuvers and failure to inhale slowly, have been documented by the literature [S. P. Newman, "Aerosol Deposition Considerations in Inhalation Therapy" Chest/88/2/August, 1985/Supplement] as contributing to a significant reduction in the number of aerosol medication particles inspired and deposited in a patient's lungs.
Impaction and deposition of aerosol medication particles on a patient's oropharynx and upper airway may also contribute to an unpleasant taste in a patient's mouth, particularly with certain medication solution or suspension formulations such as flunisolide.
In addition to high particle velocity, a significant number of large non-respirable medication particles may be produced upon discharge as a result of the medication suspension or solution formulation as well as the atomization process. As mentioned above, conventional pMDIs have used CFCs to propel the medication out of the pMDI actuator outlet. In view of environmental concerns with CFCs, there has been a growing interest in using non-CFC propellants, such as hydrofluoroalkanes (HFAs).
An inhalation valve is often used in conjunction with an aerosol medication delivery apparatus to deliver a medication in an aerosol form to a user's respiratory tract. Typically, an inhalation valve is disposed at the output end of an aerosolization chamber and prevents aerosolized medication from leaving the chamber when the inhalation valve is in a closed position. When a patient inhales, the inhalation valve opens and allows the aerosolized medication to enter the patient's respiratory tract. The inhalation valve is usually designed to close upon exhalation by the patient.
Prior art inhalation valves generally consist of a valve member and a valve seat. In some types of prior art valves, the outer perimeter of the valve member seals against the valve seat. In operation, the act of inhalation causes the outer perimeter of the valve to move away from the valve seat and allow aerosolized medication to flow through to the patient.
In another type of prior art inhalation valve, the valve member includes one or more slits that define flaps on the valve member. Typically, the valve seat has a plurality of openings defined by what is known as a spider-like framework. In operation, when the patient inhales the flaps move away from the spider-like framework to allow aerosolized medication to pass through the openings to the patient. Upon exhalation, the flaps move against the framework to cover the openings. A number of advantageous improvements and modifications can be made to these prior designs.
It is another object to provide a device which reduces the need for a patient to coordinate activation of a pMDI canister with inhalation.
It is a further object to provide a device that reduces the delivery of nonrespirable medication particles from a pMDI canister to a patient.
It is yet another object to provide a device that reduces the impaction of medication particles on a patient's oropharynx and upper airway.
It is still another object to provide a device for the delivery of aerosol medication from a pMDI canister that uses an HFA propellant instead of a CFC propellant.